1. Field of the Invention
The present invention relates to a method for improving discontinuous reception for a wireless communication system and related communication device, and more particularly, to a method for improving discontinuous reception of a Hybrid Automatic Repeat Request (HARQ) process for a wireless communication system and related communication device.
2. Description of the Prior Art
The third generation mobile telecommunications system (called 3G system) provides high frequency spectrum utilization, universal coverage, and high quality, high-speed multimedia data transmission, and also meets all kinds of QoS requirements simultaneously, providing diverse, flexible, two-way transmission services and better communication quality to reduce transmission interruption rates. However, due to demand for high-speed and multimedia applications, the next generation mobile telecommunications technology and related communication protocols have been developed.
Long Term Evolution wireless communications system (LTE system), an advanced high-speed wireless communications system established upon the 3G mobile telecommunications system, supports only packet-switched transmission, and tends to implement both Medium Access Control (MAC) layer and Radio Link Control (RLC) layer in one single communication site, such as in Node B alone rather than in Node B and RNC (Radio Network Controller) respectively, so that the system structure becomes simpler.
The MAC layer of a user equipment (UE) includes a Hybrid Automatic Repeat Request (HARQ) entity for simultaneously executing a plurality of HARQ processes for performing a plurality of data transmissions simultaneously.
According to structure of the LTE system, discontinuous reception (DRX) is utilized in the MAC layer, allowing the UE to enter a sleep mode during certain periods, and then stop monitoring a Physical Downlink Control Channel (PDCCH). Regarding a downlink (DL) HARQ process, the UE maintains an HARQ RTT Timer for providing a certain amount of Transmission Time Intervals (TTIs) for the UE to start performing a retransmission detection of the downlink HARQ process after this period. In this application, HARQ RRT timer is hereinafter abbreviated as RTT timer.
When a network terminal indicates the UE to perform a retransmission of the downlink HARQ process, the UE starts the RTT Timer and enters the sleep mode. The UE is awaked and detects whether retransmission information is sent on the PDCCH at expiry of the RTT Timer. The UE only utilizes a RTT timer to manage retransmission detection of multiple downlink HARQ processes.
Please refer to FIG. 1, which is a schematic diagram of retransmission detecting timings of a downlink HARQ process managed by a UE according to the prior art. The UE uses downlink HARQ processes A and B to receive packets 600A and 602B respectively. When the UE fails to decode the packet 600A, a RTT Timer HTR1 starts to count, and retransmission detection of the packet 600A would be started if the RTT Timer HTR1 expires at a time T1. In this period of the RTT Timer HTR1, the UE stays in the sleep mode. Generally, the UE is awaked at the time T1 for detecting the retransmission of the packet 600A. However, when the packet 602B is failed to be decoded at a time T2, the RTT timer HTR1 starts to recount and thereby expires at a time T3. In this situation, for the downlink HARQ process A of the packet 600A, an expected time the UE starts to detect the retransmission of the packet 600A is postponed from the time T1 to the time T3. If an eNB (evolved Node-B) schedules the retransmission of the packet 600A between the time T1 and T3, the UE is unable to detect the retransmission of the packet 600A, and thereby misses the chance of re-receiving data of the packet 600A.
According to the prior art, the plurality of downlink HARQ processes of the UE may delay a part of the retransmission detecting timings because the retransmission detecting timings are managed by the same RTT Timer. Thus, probability that the UE misses retransmission packets is increased, and flexibility of scheduling retransmission at the network side is reduced.